What to remember from the latest reassuring models from the Institut Pasteur

Should we fear a new wave of Covid-19 contamination? This is the question that the Pasteur Institute has tried to answer. according to one The study was published Thursday 10 Mars (PDF)Experts think so “In all of the scenarios explored, peak cases (in March) It’s still well below the January peak.”

According to a previous report by the Pasteur Institute February 21 (PDF)BA.2, a sub variant of Omicron, should not by itself have any “A significant recovery in the epidemic.” This was a throwback “possible”according to models “If the French moderate their behaviour”. However, as of Monday, March 14, many restrictions will be lifted. A mask will no longer be mandatory in school. The health protocol will no longer be applied in business. Finally, a vaccination card, as well as a mask in stores, will not be needed.

While the number of infections has been on a slight increase for a week, after a period of decline since the peak of the last wave, at the end of January, Olivier Veran reported, on Friday, March 11, that there was a jolt in the epidemic. Franceinfo is evaluating the results of these new models.

Unsurprising progression of the Omicron BA.2 . subvariable

“Our model correctly predicted the dynamics of the BA.2 ratio between Omicron states, The Pasteur Institute notes. The model predicted that 29% and 45% of Omicron cases would be BA.2 on February 14 and 21; Flash data available on March 9 indicates 25% and 40% BA.2 among Omicron cases on those dates.”

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In the last week of February, variant BA.2 already accounted for 43% of new coronavirus cases, according to public health France (PDF). According to preliminary data from the same epidemiological point, the majority should become from the first week of March (52% of new infections).

Pollution plateau arrived earlier than expected

According to February models, the Pasteur Institute “The hypothesis that the French will increase their contacts from 1 March, leading to a plateau of pollution in early March”. Most “The percentage of contamination was observed a little earlier, which indicates that these changes occurred before the first of March.”

So the French had more contacts from the end of February. The curve of Covid-19 infection is near “Forecasts obtained on the basis of the assumption that as of February 22, the French have increased their contacts by about 40% compared to the January and February levels”. This additional level of contact density, +40%, is “Slightly higher than measured in December 2021”or “Transmission rates (…) were approximately 30% higher than the January-February transmission rates”.

Transmission rates up to 130% after restrictions are lifted

In this study, the Pasteur Institute starts from hypotheses of high transmission rates. In fact, “Easing control measures on March 14 should increase transmission rates”, Institute reports.

Thus, the scenarios are based on transmission rates 50%, 70%, 100% or 130% above January and February levels.” For comparison, the connection rates were in November 2021 “About 60-70% higher” To early 2022 and December, 30% higher.

In March, the peak of cases is “much lower” than in January

The Pasteur Institute developed two scenarios. The first explores the hypothesis of relaxation of actions – thus increasing contacts March 14. corn “practically”And the “The French can expect to ease the measures” Barriers and have more contacts before March 14th. Thus, the second scenario is based on a change in habits a week before, starting on March 7.

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“In all of the scenarios explored, the peak of cases remains well below the January peak, Institute concludes. It could exceed 100,000 daily cases in March in scenarios where transmission rates increase significantly after control measures are relaxed. This will be higher than the current numbers but much lower than the numbers seen during the last wave at the end of January.

In fact, an average of 58,336 positive cases were counted per day during the week leading up to March 10. The shift is already noticeable, with 74,818 positive cases on Thursday, March 10 alone.

But that is still far from the peak of the epidemic wave at the beginning of the year, when 501,635 new infections were noted on January 25. Thus, the Basseterre Institute forecast for March is five times lower than the record of pollution observed since the beginning of the epidemic.

Forecasts likely to be ‘over-optimistic’

However, in the introduction to the study, the Pasteur Institute calls for these encouraging findings to be taken with caution, which rules out the possibility of a new pandemic wave from March.

This study did not include “The gradual deterioration of immunity, which may lead to” Expectations “Very optimistic”. like that, ‘climate effect’ These models are not taken into account.

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